Because of their widely ranging mechanical properties and their ability to be relatively easily machined and formed, plastic foams and elastomers have found wide use in a multitude of industrial and consumer applications. In particular, urethane foams and elastomers have been found to be well suited for many applications. Automobiles, for instance, contain a number of components, such as cabin interior parts, that are comprised of urethane foams and elastomers. Such urethane foams are typically categorized as flexible (or semi-rigid) or rigid foams; with flexible foams generally being softer, less dense, more pliable and more subject to structural rebound subsequent loading than rigid foams.
The production of urethane foams and elastomers is well known in the art. Urethanes are formed when NCO groups react with hydroxyl groups. The most common method of urethane production is via the reaction of a polyol and an isocyanate which forms the backbone urethane group. A cross linking agent may also be added. Depending on the desired qualities of the final urethane product, the precise formulation may be varied. Variables in the formulation include the type and amounts of each of the reactants.
In the case of a urethane foam, a blowing agent is added to cause gas or vapor to be evolved during the reaction. The blowing agent creates the void cells in the final foam, and may be a relatively low boiling solvent or water. A low boiling solvent evaporates as heat is produced during the isocyanate/polyol reaction to form vapor bubbles. If water is used as a blowing agent, a reaction occurs between the water and the isocyanate group to form an amine and CO.sub.2 gas in the form of bubbles. In either case, as the reaction proceeds and the material solidifies, the vapor or gas bubbles are locked into place to form void cells. Final urethane foam density and rigidity may be controlled by varying the amount or type of blowing agent used.
A cross-linking agent is often used to promote chemical cross-linking to result in a structured final urethane product. The particular type and amount of cross-linking agent used will determine such final urethane properties such as elongation, tensile strength, tightness of cell structure, tear resistance and hardness. Generally, the degree of cross-linking that occurs correlates to the flexibility of the final foam product. Relatively low molecular weight compounds with greater than single functionality are found to be useful as cross-linking agents.
Catalysts may also be added to control reaction times and to effect final product qualities. The effects of catalysts generally include the speed of the reaction. In this respect, the catalyst interplays with the blowing agent to effect the final product density; the reaction should proceed at a rate such that maximum gas or vapor evolution coincides with the hardening of the reaction mass. Also, the effect of a catalyst may include a faster curing time, so that a urethane foam may be produced in a matter of minutes instead of hours.
Polyols used in the production of urethanes are petrochemicals, being generally derived from ethylene glycol. Polyester polyols and polyether polyols being the most common polyols used in urethanes production. For semi-rigid foams, polyester or polyether polyols with molecular weights of from 3,000 to 6,000 are generally used, while for flexible foams shorter chain polyols with molecular weight of from 600 to 4,000 are generally used. There is a very wide variety of polyester and polyether polyols available for use, with a particular polyols being used to engineer and produce a particular urethane elastomer or foam having desired particular final toughness, durability, density, flexibility, compression set ratios and modulus and hardness qualities. Generally, lower molecular weight polyols and lower functionality polyols tend to produce more flexible foams than do heavier polyols and higher functionality polyols. In order to eliminate the need to produce, store, and use different polyols, it would be advantageous to have a single versatile component that was capable of being used to create final urethane foams of widely varying qualities.
Further, use of petrochemicals such as polyester or polyether polyols is disadvantageous for a variety of reasons. As petrochemicals are ultimately derived from petroleum, they are a non-renewable resource. The production of a polyol requires a great deal of energy, as oil must be drilled, extracted from the ground, transported to refineries, refined and otherwise processed to yield the polyol. These required efforts add to the cost of polyols, and to the disadvantageous environmental effects of its production. Also, the price of polyols tends to be somewhat unpredictable as it tends to fluctuate based on the fluctuating price of petroleum.
Also, as the consuming public becomes more aware of environmental issues, there are distinct marketing disadvantages to petrochemical based products. Consumer demand for "greener" products continues to grow.
It would therefore be most advantageous to replace polyester or polyether polyols as used in the production of urethane elastomers and foams with a more versatile, renewable, less costly, and more environmentally friendly component.
Efforts have been made to accomplish this. Plastics and foams made using fatty acid triglycerides derived from vegetables have been developed, including soy bean derivatives. Because soy beans are a renewable, relatively inexpensive, versatile, and environmentally friendly, they are desirable as ingredients for plastics manufacture. Soy beans may be processed to yield fatty acid triglyceride rich soy oil and a protein rich soy flour.
Unlike urethanes, many plastics are protein based. For these types of plastics, soy protein based formulations have been developed. U.S. Pat. No. 5,710,190, for instance, discloses the use of soy protein in the preparation of a thermoplastic foam. Such plastics, however, are not suitable for use in applications that call for the particular properties of urethanes. Since urethanes don't utilize proteins in their formulations, soy proteins are not relevant for urethane manufacture.
Epoxidized soy oils in combination with polyols have also been used to formulate plastics and plastic foams, including urethanes. For example, U.S. Pat. No. 5,482,980 teaches use of an epoxidized soy oil in combination with a polyol to produce a urethane foam. A polyester or polyether polyol remains in the formulation, however. Also, as the epoxidation processing of the soy oil requires energy, materials and time, use of an un-modified soy oil would be more advantageous.
Efforts have been made to produce a urethane type cellular plastic from un-modified soy oil. U.S. Pat. Nos. 2,787,601 and 2,833,730 disclose a rigid cellular plastic material that may be prepared using any of several vegetable oils, including soy oil. The foam disclosed in these patents, however, is made from a multistep process requiring the preparation of a pre-polymer and, in the case of U.S. Pat. No. 2,833,730, relatively low cross-linker concentrations are urged, resulting in questionable product stability. Further, use of a particular isocyanate, namely toluene diisocyanate, is disclosed which is disadvantageous due to its relatively high toxicity.
An unresolved need therefore exists in industry for a urethane elastomer and a flexible urethane foam, and a method of producing such materials, that are based on a reaction between isocyanates and a relatively inexpensive, versatile, renewable, environmentally friendly material such as vegetable oils as a replacement for polyether or polyester polyols.